Drain pipes for preventing landslides and method for driving the same

ABSTRACT

A drain pipe is disclosed which comprises a drain pipe section provided with a plurality of weep holes or slots and a shielding pipe section slidably fitted over the drain pipe section and adapted to remain in such a position with respect to the drain pipe section as to completely shield the weep holes or slots thereof when driven into the ground. After the drain pipe section has been driven into a predetermined depth, the shielding pipe section is further driven into the ground while the drain pipe section remains stationary, so that the weep holes or slots are exposed to a cylinderical cavity left therearound by the shielding pipe section.

Uited States Patent 1 1 1 Watanahe 11 1 Sept. 2, 1975 [54] DRAIN PIPES FOR PREVENTING 166,136 7/1875 Patterson 175/22 LANDSLIDES AND METHOD FOR DRIVING 2333;? 2x23? i en 61; 8. THE SAME 1,481,219 1/1924 Miller 173/33 [76] Inventor: Hikoitsu Watanabe, No. 5-13, 1,866,826 3 S h nn 6 /35 X l chone Ebara cho Nakano ku Wallace; Tokyo Japan 3,103,789 9/1963 McDufi et a1. 61/1l 3,407,607 10/1968 Jordan 61/11 [22] 1973 FOREIGN PATENTS OR APPLICATIONS [211 APPL 391,984 287,808 4 1953 Switzerland 61/11 [30] Foreign Application Priority Data Primary Examiner j acob P Aug. 29, 1972 Japan 47-85883 Atwmey Agent Jews Feb. 12, 1973 Japan.,.. 48-16526 Mar. 27, 1973 Japan 48-34091 [57] ABSTRACT July 17, 1973 Japan 48-79949 A drain p pe is disclosed which comprises a drain P p July 27, 1973 Japan 48-75530 section provided i h a pl r lity f weep holes or slots and a shielding pipe section slidably fitted over the [52] U.S. Cl. 61/35; 61/1 1; 61 /53.7; r n pip t n n ap ed to remain in such a po- 173/33; 175/19; 175/17] sition with respect to the drain pipe section as to com- [51] Int. Cl.'-' E02B 11/00; E21B 11/02 p y Shield the w p h l s or lots thereof when [58] Field of Search 61/35, 36, 11, 13, 53.7; driven into the ground. After the drain P p section 175/19, 22, 171; 166/227; 173/33 has been driven into a predetermined depth, the shielding pipe section is further driven into the ground [56] References Cited while the drain pipe section remains stationary, so that UNITED STATES PATENTS the weep holes or slots are exposed to a cylinderical cavity left therearound by the shielding pipe section. 76,485 4/1868 Martln 175/22 80,504 7/1868 Rhoades et al. 175/19 X 9 Claims, 29 Drawing Figures PATENTED W 21975 mm mm mm mm SHEET PATENTEU BE? 2 I975 uvm,

PATENTED SEP 21975 S'riEET dd TL PATENTEI] SEP 2 I975 DRAIN PIPES FOR PREVENTING LANDSLIDES AND METHOD FOR DRIVING THE SAME BACKGROUND OF THE INVENTION:

The present invention relates to drain pipes for driving into the natural slopes. earth dams or enbankments in which landslides tend to occur in order to drain excessive seeping water so that the water content may be maintained at a safe level, the drain pipes being driven into the ground without disturbing the stability of the slopes or the like.

The true causes of landslides have not been clarified yet, but it is well known that a sudden landslide is triggered by a heavy rain because the seeping water becomes in excess of the maximum allowable permeability of the soil, sand and rocks. Therefore it must be a very effective countermeasure against landslides to drain excessive seeping water in the slopes or embankments so that the water content may be always maintained at a safe level. In this case it is imperative to drive drain pipes into the slopes or the like without adversely affecting the stability thereof.

In view of the above there has been proposed a method for driving drain pipes of the type having one or leading end terminated into a cone-shaped point and being provided with a plurality of weep holes or slots. The drain pipe is set horizontally or inclined downwardly toward the open end, and, if required, is joined to an extension pipe or pipes so that the drain pipe may be set to a predetermined depth. However, when the drain pipe is driven into the ground the soil and sand enters into the drain pipe through the ,weep slots or holes so that clogging of the drain pipe tends to very frequently occur. As a result. even when the drain pipe is set to a predetermined depth it serves no useful purpose at all. In order to overcome this problem, there has been proposed a method for charging water by a pump into the driven drain pipe, thereby mixing clogging soil or sand with water to discharge it outside of the drain pipe. This step is repeated many times until the clogged weep holes or slots are opened and a cavity or cavities are formed around the weep holes or slots by the erosin of soil or sand surrounding them, by the charged water. Thus, water collected in the cavities may be discharged through the weep holes or slots, the drain pipe and the extension pipe or pipes. However, the quantity of soil or sand which is discharged by the pumped water is very limited and the operation is time consuming and requires much labor. Furthermore the operation is extremely difficult when a drain pipe is driven very deep into the ground.

SUMMARY OF THE INVENTION:

In view of the above one of the objects of the present invention is to provide an improved drain pipe for preventing landslides which may substantially eliminate the defects encountered in the conventional drain pipes.

According to one embodiment of the present invention a drain pipe comprises drain pipe section having a drill section attached to the leading end thereof and provided with a plurality of axial weep slots and a shielding pipe section slidably fitted over the drain pipe section and having a sufficient length to completely shield the weep slots. When the drain pipe is driven into the ground the shielding pipe section is adapted to remain in such a position as to completely shield the weep slots of the drain pipe section. After the drain pipe has been set to a predetermined depth a driving rod is inserted through the drain pipe section or sec tions and extension pipes so that the driving impact may be applied only to the shielding pipe section. As a result the shielding pipe section is further driven into the ground while the drain pipe section remains completely stationary so that the weep slots may be exposed to a cylindrical cavity left therearound by the shielding pipe section.

The above and other objects, features and advantages of the present invention will become more apparent from the following description of some preferred embodiments thereof taken in conjection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of first embodiment of a drain pipe in accordance of the present invention with a shielding pipe section being remained in a position for shielding weep slots of a drain pipe section;

FIG. 2 is a side view thereof with the shielding pipe section being further driven so as to expose the weep slots;

FIG. 3 is a side view of the drain pipe section;

FIG. 4 is a side view of the shielding pipe section;

FIG. 5 is a top view thereof;

FIG. 6 is a side view illustrating the drain pipe driven into the ground the joined to an extension pipe;

FIG. 7 is a side view of a driving rod assembly used for driving further the shield pipe section;

FIG. 8 shows the drain pipe set into the ground;

FIG. 9 is a perspective view of a driving apparatus;

FIG. 10 is a diagrammatic view illustrating the interior of a motor-driven hammer thereof;

FIG. 11 is a side view thereof;

FIGS. 12 and 13 are side views of the driving apparatus shown in FIG. 9 illustrating the steps of driving the drain pipe;

FIGS. 14 and 15 are perspective view illustrating another driving appratus and the steps of driving the drain P p FIG. 16 shows the drain pipes of the present invention driven into a slope;

FIG. 17 is a cross sectional view thereof;

FIG. 18 is a sectional view of a second embodiment of a drain pipe in accordance with the present invention;

FIG. 19 is a side view of the drain pipe section of the second embodiment;

FIG. 20 is a side view of a shielding pipe section thereof;

FIG. 21 is a top view thereof;

FIG. 22 is a side view of an impact transmission member;

FIG. 23 is a top view thereof;

FIG. 24 is a sectional view of a third embodiment of a drain pipe in accordance with the present invention;

FIG. 25 is a sectional view of a drain pipe section thereof;

FIG. 26 is a sectional view ofa shielding pipe section thereof; and

FIGS. 2729 are side views illustrating the steps of driving the drain pipe shown in FIG. 24.

DESCRIPTION OF THE PREFERRED EMBODIMENTS:

First Embodiment, FIGS. l4

First referring to FIG. I, a drain pipe 30 in accordance with the present invention is shown as generally comprising a drain pipe section 31 and a shielding pipe section 32.

As best shown in FIG. 3, the drain pipe section 31 consists of a steel pipe having a desired length and diameter and is provided with four equiangularly spaced axial weep slots 33 extending from the rear end of the drain pipe section 31 over a predetermined length. A coupling or socket 34 is screwed over the rear end of the drain pipe section 31 in order to join the drain pipe section 31 to an extension pipe to be described in more detail hereinafter. The leading end of the drain pipe section 31 terminates in a drill section 36 having four cutting edges 35 equiangularly spaced from each other.

As best shown in FIGS. 4 and 5 the shielding pipe section 32 has an inner diameter so that it may be slidably fitted over the drain pipe section, 31 and such a length as to shield the weep slots 33 of the drain pipe section 31 when fitted thereover. The rear end of the shielding pipe section 32 terminates into a cross-shaped impact receiving member 37 with four ridges which are adapted to be loosely fitted into the weep slots 33 of the drain pipe section 31 when the shielding pipe section 32 is fitted over the drain pipe section 31.

In assembly the shielding pipe section 32 is fitted over the drain pipe section 31 with the edges of the impact receiving member 37 fitted into the weep slots 33 of the drain pipe section 31, and thereafter the coupling or socket 34 is screwed to the rear end of the drain pipe section 31. Then, the shielding pipe section 32 is slidable over the drain pipe section 31, and when the impact receiving member 37 is in abuttment with the coupling or socket 34 it may completely shield the weep slots 33 of the drain pipe section 31 as best shown in FIG. 1. On the other hand when the shielding pipe section 32 abuts against the rear end of the drill section 36 the weep slots 33 are completely exposed as best shown in FIG. 2.

Driving Apparatus, FIGS. 9-15 Next referring to FIGS. 9l5, the driving apparatus generally indicated by 50 and 51 for driving the drain pipe of the type described hereinbefore into the ground will be described hereinafter. The driving apparatus 51 shown in FIGS. 9-13 is used for driving the drain pipes of the present invention into the ground relatively close to the base of the slope whereas the driving apparatus 51 shown in FIGS. 14 and is used for driving the drain pipes into the slope except the place where the driving apparatus 50 is applicable.

Referring to FIG. 9 the driving apparatus generally indicated by 50 comprises three supports 54a, 54/), and 54:- each of which consists of a top brace member 52 and a pair of legs 53 joined to pedestals 56, respectively, through turnbuckles so that the height of each leg 53 may be adjustable. An anchor pile 57 is driven into the ground through a hole formed through the pedestal 56 so that the pedestal 56 may be securely held in position. A socket 58 is securely fixed to the top brace member 52 at the center thereof for receiving therein the end ofa guide rod 59 ofa desired length. The guide rods 59 are securely held in the sockets 58 by means of bolts 60. Therefore the supports 54a, 5412 and 54c may be spaced apart by a predetermined distance from each other and held securely upon the ground.

The driving apparatus 50 further comprises a movable frame generally indicated by 61 and adapted to move along the guide rods 59. The movable frame 61 comprises a horizontal beam carried by carriages 67, a vertical rod 62 extending downwardly from the end of the horizontal beam remote from the right carriage 67 and having its lower end terminated into a guide plate 64 with a drain pipe guide hole 63, and a pair of quadrant guide members 65 having their ends joined to the horizontal and vertical beams, respectively. The pair of guide members 65 also serve as brace members between the horizontal and vertical beams 61 and 62, and guide a pendulum rod 69 of a motor-driven hammer 66 to be described in more detail hereinafter. The carriages 67 are similar in construction, and each comprises a pair of frames 67 having a roller 68 attached thereto. The rollers 68 ride on the guide rods 59 so that the movable frame 61 may be movable in parallel with the guide rods 59 as the drain pipe 30 is driven into the ground in a manner to be described in more detail hereinafter.

In order to'drive the drain pipe 30 into the ground, the pendulum-like motor-driven hammer 66 suspended by the pendulum rod 69 which in turn is pivoted to the right carriage 67 with a pivot 70 and is guided by the guide members 65 so as to prevent lateral movement is provided.

Next referring to FIGS. 10 and 11 the motor-driven hammer 66 will be described. Within a housing 71 a pair of motors 73 are mounted upon a mount 72, and a winch comprising a drum 77 with a wire rope 78 wound therearound and a clutch 76 is loosely supported by a shaft which in turn in supported by a pair of brackets 74 securely fixed to the mount 72. The rotation of each motor 73 is transmitted to the shaft 75 through a belt drive consisting ofa drive pulley 80 fixed to a driving shaft of the motor 73, a driven pulley 81 fixed to the shaft 75 and an endless belt 82 wrapped around the driving and driven pulleys 80 and 81.

The right clutch section 76 which is loaded with a spring 91 is provided with an annular groove 83 into which is fitted a pin 85 extending from one end of an actuating or operating lover 84 which is pivoted to the base 72 with a pin 86 and whose the other end is pivoted to a plunger with pin 88 ofa plunger and solenoid assembly 87. Therefore, as the plunger and solenoid assembly 87 is energized or de-energized the right clutch section 76 is slidably moved along the shaft 75 to engage with or disengage from the mating left clutch section 89.

One end of the wire rope 78 is securely fixed to the drum 77 whereas the other end is fixed to an ear 90 fixed to the horizontal beam 61 (See FIG. 9).

A brace rod 92 which is joined to the brackets 74 serves to ensure that the wire rope 78 will be wound around the drum 77.

When the motors 73, which are supplied with power through a cable 93, are driven, their rotation is transmitted to the clutch section 76 through the driving pulley 80, the endless belt 82, the driven pulley 81 and the shaft 75. When the clutch section 76 is engaged with the mating clutch section 89 as the plunger and solenoid assembly 87 is energized, the drum 72 which is loosely fitted over the shaft 75 is rotated to wind the wire rope 78 thcraround. As a consequence the motordrivcn hammer 66 is swung about the pin 70 upwardly. Whcn the solenoid 87 is dc-encrgized when the motordrivcn hammer 66 is lifted to a predetermined height, the right clutch section 86 is disengaged from the left clutch section 89 so that the free rotation of the drum 77 is permitted. As a result the motor-driven hammer 66 swings back to drive the drain pipe 30 as shown in FIG. 12. The pendulum-like driving operation is cycled so that the drain pipe 30 is gradually driven into the ground as shown in FIG. 13.

The driving apparatus 51 which will be described hereinafter with reference to FIGS. 14 and is sub stantially similar in construction to the driving apparatus 50, except its supports or supporting frames are different. As shown in FIG. 14 the left end of the guide rod 94 is joined to a pipe 96 with a bolt 97 of a foot member 95 securely held in position on the slope by means of anchor piles 109. The right end of the guide rod 9 1 is supported by a supporting frame generally indicated by 103. The supporting frame 103 comprises an inverted U-shaped upper leg 99 whose lower end portions are telescopically fitted into lower legs 101 whose lower ends are securely fixed to pedestals 100 which in turn are securely held in position by means of the anchor piles 109. The height of the supporting frame 103 is therefore adjustable and the inverted U- shaped leg 99 can be securely held in position relative to the lower legs 101 by means of bolts 102.

The supporting frame 103 is further supported by a pair of telescopic brace means, each comprising an inner brace rod 105 whose one end is pivoted to the inverted U-shaped leg 99 with a pin or rivet 104 and whose the other end portion is telescopically fitted into and securely held in position with respect to an outer brace pipe 107 with a bolt 108. The outer brace pipe 107 is securely fixed to a foot which in turn is securely held in position on the slope by means of the anchor piles 109. The length of the telescopic brace means is therefore adjustable. Furthermore stay wire ropes or chains 1 10 are extended from anchor bolts (not shown) driven into the ground on the slope and are fixed to hooks 111 fixed to the pedestals 100 so that the pedestals 100 may be further securely held in position.

The movable frame 61 and the pendulumlike motordriven hammer 66 are mounted in a manner substantially similar to that of the driving apparatus 50, but it should be noted that the motor-driven hammer 66 is not suspended from the carriage 67 but from a suspending frame 112 fixed to the horizontal beam 61, that instead of the guide plate 64 a U-shaped guide member 64 made of a rod is used and that the guide members 65 are straight. The above arrangements different from those of the driving apparatus 50 are merely a matter of design, and both the driving apparatus 50 and 51 are based upon the same principle.

The driving apparatus 50 or 51 is used to drive the drain pipes 30 into the slope. depending upon the posi tions on the slope where the drain pipes 30 are driven. In operation the movable frame 61 is moved to the initial or right position as shown in FIGS. 12 and 14, and the drain pipe 30 to be driven is inserted through the guide plate or member 64 so that the drill section of the drain pipe 30 may be placed in correct position. Thereafter, an impact receiving cap 114 is screwed to the rear end of the drain pipe section 31, so that the starting position of the guide member or plate 64 and hence of the movable frame 61 is automatically determined. Thereafter, the motor-driven hammer 66 is operated in the manner described hereinbefore to give the driving impact to the impact receiving cap 1114, thereby driving the drain pipe 30 into the ground. As the drain pipe 30 is driven into the ground the movable frame 61 and hence the motor-driven pendulum hammer 66 are automatically advanced because of the engagement of the impact receiving cap 114 with the guide plate or member 64 as shown in FIGS. 13 and 15.

As the drain pipe 30 is driven into the ground the shielding pipe section 32 slidably fitted over the drain pipe section 31 makes contact with the surface of the ground before the closed ends of the weep slots 33 of the drain pipe section 31 are driven into the ground so that the shielding-pipe section 32 remains undriven into the ground while the drain pipe section 31 is driven into the ground. When the rear end of the shielding pipe section 32 contacts with the coupling or socket 34, the driving impact is also transmitted to the shielding pipe section 32 so that it is driven into the ground together with the drain pipe section 31 as shown in FIG. 1. Before the coupling or socket 34 is driven into the ground, the driving operation is suspended to remove the cap 14, thereby releasing the guide member or plate 64 from the drain pipe 30. Thereafter an extension pipe 115 is joined to th'e drain pipe 30, passed through the guide member or plate 64, and has its outer end screwed to the impact receiving cap 66. Then the extension pipe 115 is driven into the ground with the drain pipe 30 in the manner described hereinbefore. Any desired number of extension pipes 115 may be joined and driven into the ground as shown in FIG. 6 so that the drain pipe 30 may be driven to a predetermined depth. When the drain pipe 30 is driven the shielding pipe section 32 remains in engagement with the coupling 34 because of the resistance encountered from the soil so that the weep slots 33 may be completely covered by the shielding pipe section 32 and soil or sand is prevented from entering into the drain pipe 30 through the weep slots 33 thereof.

After the drain pipe 30 together with the extension pipes 115 are set to a desired depth, a plurality of solid steel rods 116 with a suitable length are joined to a suitable length. That is, each solid steel rod 116 has an in ternally threaded hole and an externally threaded projection so that the externally threaded projection may be screwed into the internally threaded hole as shown at' 117 in FIG. 7. The outer diameter of the steel rods 116 is so selected that the steel rod assembly may be slidably fitted into the extension pipes 115, and the length of the steel rod assembly is so selected that is ex tends out of the last extension pipe 115 by a predetermined length for the reason to be described hereinafter when the leading end of the jointed steel rods 115 is in engagement with the cross-shaped impact receiving member 37 of the shielding pipe section 32. The driving impact is applied to the steel rod assembly 115 in the manner described hereinbefore so that only the shielding pipe section 32 is driven further into the ground until it abuts against the drill section 36 while the drain pipe section 31 remains stationary as shown in FIG. 8. As a consequence the weeping slots 33 of the drain pipe section 31 are exposed and a cylindrical cavity 118 is formed around them as shown in FIG. 8. When the steel rod assembly 115 is withdrawn, the drain pipe driving operation is completed.

FIGS. 16 and 17 illustrate the drain pipes and extension pipes driven into the slope 113 where there is a danger of landslide. Since the weep slots 33 are all exposed and the cylindrical cavities 118 are formed around them, the excessive seeping water is discharged at a level at which no landsliding will occur. The drain pipes 30 and the extension pipes 115 are driven into the slope without adversely affecting the inherent stability thereof. In some cases, because of the poor permeability of the soil the excessive seeping water cannot be drained satisfactorily even when many drain pipes are driven. To overcome this problem weep holes 119 may be drilled from the crown of the slope by any conventional method and filled with sand to form vertical sand drains.

Second Embodiment of Drain Pipe, FIGS. 1823 Next referring to FIGS. 18-23, the second embodiment of the drain pipe of the present invention will be described hereinafter. Briefly stated, the second embodiment 30a is similar in construction to the first embodiment except (a) that the drain pipe section 310 is provided with only a pair of opposed axial weep slots 33a, (/2) that the cross-shaped impact receiving member 37a of the shielding pipe section 32a has therefore a pair of opposed ridges adapted to be loosely fitted into the weep slots and a pair of opposed short ridges which are spaced apart from the inner wall of the shielding pipe section 32a so that the drain pipe section 31a may be loosely fitted between the inner wall of the shielding pipe section 32a and the leading edges of the short ridges, and (c) that the coupling or socket 34a may be detachably attached to both ends of the drain pipe section 31a whereas the drill section 360 may be also attached to the leading end of the drain pipe section 31a.

In driving operation, after the shielding pipe section 32a is fitted over the drain pipe section 3111, the drill section 36a and the coupling or socket 34a are screwed to the ends of the drain pipe section 31:: respectively. The drain pipe 30:: may be driven into the ground in a manner substantially similar to that of the first embodiment by the driving apparatus 50 or 51, but according to the second embodiment instead of extension pipe 115 another drain pipe 30a may be joined to the first drain pipe 30:: through the coupling or socket 34a. In this case an impact transmission member 39 is inserted into the second drain pipe section 33a as best shown in FIG. 18. As shown in F IGS.'22 and 23 the impact transmission member 39 has a length substantially equal to the distance between the cross-shaped impact receiving members 3711 of the first and second drain pipe sections 330 and is provided with at least three fin-like positioning members 38 so that the impact transmission member 39 may be positioned substantially coaxially of the drain pipe section 31a. In like manner a desired number of drain pipes 3011 may be joined and driven into a predetermined depth as shown in FIG. 18. Thereafter a steel rod 116a which is longer than the shielding pipe section 32a or the weep slots 33a is inserted into the last drain pipe section 310 to drive the cross-shaped impact receiving member 370 thereby driving further the shielding pipe section 32:: into the ground over the drain pipe section 31a so as to expose the weep slots 33a. The driving impact is successively transmitted to the cross-shaped impact receiving members 3711 of the successive shielding pipe sections 32a through the impact transmission members 39 so that all of the shielding pipe sections 3211 may be further driven into the ground while the drain pipe sections 31:: remain stationary. Therefore all of the weep slots 33a are exposed and the cylindrical cavities 118 are formed therearound with the case of the first embodiment.

Third Embodiment of Drain Pipe, FIGS. 24-29 In the first and second emboidments described hereinbefore the drill section 36 or 36a is attached to the leading end of the drain pipe section 33 or 33a, but in the third embodiment a drill section 46 is attached to the leading end of the shielding pipe section 41 as shown in FIGS. 24 and 25. The length of the shielding pipe section 42 is so selected that when it is fitted over the drain pipe section 41 its trailing or rear end abuts against the socket or coupling 49 screwed to the rear end of the drain pipe section 41 whereas the leading end of the drain pipe section 41 makes a slight contact with the inner surface of the drill section 46. The drain pipe section 41 is provided with a plurality of weep holes 43 as best shown in FIG. 25.

In driving operation the driving impact is transmitted from the socket or coupling 47 of the drain pipe section 41, joined or not joined to the extension pipe 115, to the drill section 46 of the shielding pipe section 42 so that the drain pipe generally indicated by 40 is driven into the ground as shown in FIG. 27. After the drain pipe 40 and the extension pipe or pipes have been driven to a predetermined depth, an operating steel rod 116 having a suitable length is inserted into the extension pipes 115 and the drain pipe section 41, and thereafter the driving impact is exerted to the operating steel rod 116 so that the operating steel rod 116 pushes the drill section 46 so as to drive only the shielding pipe section 42 into the ground while the drain pipe section 41 remains stationary as shown in FIG. 28. As a result the weep holes 43 of the drain pipe section 41 are all exposed and the cylindrical cavity is formed around them as with the case of the first and second embodiment as shown in FIG. 29.

So far the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawing, but it is to be understood that variations and modifications may be effected without departing the true spirit of the present invention.

What is claimed is:

1. A drain unit for draining a sloping ground formation and thus preventing landslides due to excess ground water by installing said drain unit at a slight upward inclincation relative to the horizontal, comprising a drain pipe having a plurality of circumferentially distributed openings and adapted to be driven into the sloping ground at said inclination;

a shielding pipe telescoped over and slidably surrounding said drain pipe and covering said openingsthereof; and

connecting means connecting the telescopedtogether pipes forjoint driving thereof at said inclination into the sloping ground formation to a desired depth, and for thereafter driving said shielding pipe alone beyond said desired depth so as to displace said shielding pipe forwardly with reference to said drain pipe and expose said opening while leaving about said drain pipe in the region of said openings an annular clearance in which the soil is substantially spaced from said drain pipe.

2. A method of preventing landslides by draining water from sloping ground, comprising the steps of driving into the sloping ground at an upward angle relative to the horizontal an assembly composed of a drain pipe having apertures, and a shielding pipe telescoped over said drain pipe and covering said apertures;

discontinuing driving of said assembly when the same has reached a desired depth; and

thereafter driving said shielding pipe alone deeper into the ground so as to axially displace said shielding pipe relative to and forwardly of said drain pipe to thereby expose said apertures in the drain pipe while simultaneously forming an annular clearance about the drain pipe in which the soil is substantially spaced from said drain pipe.

3. A method as defined in claim 2; and further comprising the step of drilling weep-holes into the sloping ground in substantially vertical direction, and filling said weep-holes with sand, so as to improve the permeability of the ground to water and facilitate the run-off of the water into said drain pipe.

4. A drain unit for draining a sloping ground formation and thus preventing landslides due to excess ground water by installing said drain unit at a slight upward inclinations relative to the horizontal, comprising a drain pipe having a plurality of circumferentially distributed slots and adapted to be driven into the sloping ground at said inclinations;

a shielding pipe telescoped over and slidably surrounding said drain pipe and covering said slots thereof; and

connecting means connecting the telescopedtogether pipes for joint driving thereof at said inclinations into the sloping ground formation to a de sired depth, and for thereafter driving said shielding pipe alone beyond said desired depth so as to displace said shielding pipe forwardly with reference to said drain pipe and expose said said slots while leaving about said drain pipe in the region of said slots an annular clearance in which the soil is substantially spaced from said drain pipe.

5. A drain unit as defined in claim 4; and further comprising soil-displacing means mounted on a leading end of said drain pipe when said pipes are jointly being driven into the ground.

6. A drain unit as defined in claim 4; and further comprising a string of extension pipes for extending the length of said drain pipe; and coupling means for coupling said extension pipes to one another and to said drain pipe.

7. A drain unit for draining a sloping ground formation and this preventing landslides due to excess ground water by installing said drain unit at a slight upward inclinations relative to the horizontal, comprising a drain pipe having a plurality of circumferentiall distributed openings and adapted to be driven intc the sloping ground at said inclinations, said openings being e'qui-angularly spaced about said drain pipe and extending from a trailing end towards a leading end thereof;

a shielding pipe telescoped over and slidably surrounding said drain pipe and covering said openings thereof; and

connecting means connecting the telescopedtogether pipes for joint driving thereof at said inclination into the sloping ground formation to a desired depth, and for thereafter driving said shielding pipe alone beyond said desired depth so as to displace said shielding pipe forwardly with reference to said drain pipe and expose said openings while leaving about said drain pipe in the region of said openings an annular clearance in which the soil is substantially spaced from said drain pipe, said connecting means comprising a member mounted on the rear end of said shielding pipe and having fins slidably received in the respective openings of said drain pipe.

8. A method of preventing landslides by draining water from sloping ground, comprising the steps of providing a drain pipe assembly composed of a drain pipe having apertures, and a shielding pipe telescoped over said drain pipe and covering said apertures;

suspending said drain pipe at two axially spaced locations thereof in a substantially horizontal orientation, so that said drain pipe can perform axial swinging movements;

executing blows upon a trailing end of said drain pipe for driving said head and drain pipe substantially horizontally into the sloping ground;

discontinuing driving of said assembly when the same has reached a desired depth; and

thereafter driving said shielding pipe alone deeper into the ground so as to axially displace said shielding pipe relative to and forwardly of said drain pipe to thereby expose said apertures in the drain pipe while simultaneously forming an annular clearance about the drain pipe in which the soil is substan tially spaced from said drain pipe.

9. A method as defined in claim 8, wherein the step of suspending comprises suspending said drain pipe so that said leading end hangs at a slight upward inclination relative to the horizontal. 

1. A drain unit for draining a sloping ground formation and thus preventing landslides due to excess ground water by installing said drain unit at a slight upward inclincation relative to the horiZontal, comprising a drain pipe having a plurality of circumferentially distributed openings and adapted to be driven into the sloping ground at said inclination; a shielding pipe telescoped over and slidably surrounding said drain pipe and covering said openings thereof; and connecting means connecting the telescoped-together pipes for joint driving thereof at said inclination into the sloping ground formation to a desired depth, and for thereafter driving said shielding pipe alone beyond said desired depth so as to displace said shielding pipe forwardly with reference to said drain pipe and expose said opening while leaving about said drain pipe in the region of said openings an annular clearance in which the soil is substantially spaced from said drain pipe.
 2. A method of preventing landslides by draining water from sloping ground, comprising the steps of driving into the sloping ground at an upward angle relative to the horizontal an assembly composed of a drain pipe having apertures, and a shielding pipe telescoped over said drain pipe and covering said apertures; discontinuing driving of said assembly when the same has reached a desired depth; and thereafter driving said shielding pipe alone deeper into the ground so as to axially displace said shielding pipe relative to and forwardly of said drain pipe to thereby expose said apertures in the drain pipe while simultaneously forming an annular clearance about the drain pipe in which the soil is substantially spaced from said drain pipe.
 3. A method as defined in claim 2; and further comprising the step of drilling weep-holes into the sloping ground in substantially vertical direction, and filling said weep-holes with sand, so as to improve the permeability of the ground to water and facilitate the run-off of the water into said drain pipe.
 4. A drain unit for draining a sloping ground formation and thus preventing landslides due to excess ground water by installing said drain unit at a slight upward inclinations relative to the horizontal, comprising a drain pipe having a plurality of circumferentially distributed slots and adapted to be driven into the sloping ground at said inclinations; a shielding pipe telescoped over and slidably surrounding said drain pipe and covering said slots thereof; and connecting means connecting the telescoped-together pipes for joint driving thereof at said inclinations into the sloping ground formation to a desired depth, and for thereafter driving said shielding pipe alone beyond said desired depth so as to displace said shielding pipe forwardly with reference to said drain pipe and expose said said slots while leaving about said drain pipe in the region of said slots an annular clearance in which the soil is substantially spaced from said drain pipe.
 5. A drain unit as defined in claim 4; and further comprising soil-displacing means mounted on a leading end of said drain pipe when said pipes are jointly being driven into the ground.
 6. A drain unit as defined in claim 4; and further comprising a string of extension pipes for extending the length of said drain pipe; and coupling means for coupling said extension pipes to one another and to said drain pipe.
 7. A drain unit for draining a sloping ground formation and this preventing landslides due to excess ground water by installing said drain unit at a slight upward inclinations relative to the horizontal, comprising a drain pipe having a plurality of circumferentially distributed openings and adapted to be driven into the sloping ground at said inclinations, said openings being equi-angularly spaced about said drain pipe and extending from a trailing end towards a leading end thereof; a shielding pipe telescoped over and slidably surrounding said drain pipe and covering said openings thereof; and connecting means connecting the telescoped-together pipes for joint driving thereof at said inclination into the sloping ground formatioN to a desired depth, and for thereafter driving said shielding pipe alone beyond said desired depth so as to displace said shielding pipe forwardly with reference to said drain pipe and expose said openings while leaving about said drain pipe in the region of said openings an annular clearance in which the soil is substantially spaced from said drain pipe, said connecting means comprising a member mounted on the rear end of said shielding pipe and having fins slidably received in the respective openings of said drain pipe.
 8. A method of preventing landslides by draining water from sloping ground, comprising the steps of providing a drain pipe assembly composed of a drain pipe having apertures, and a shielding pipe telescoped over said drain pipe and covering said apertures; suspending said drain pipe at two axially spaced locations thereof in a substantially horizontal orientation, so that said drain pipe can perform axial swinging movements; executing blows upon a trailing end of said drain pipe for driving said head and drain pipe substantially horizontally into the sloping ground; discontinuing driving of said assembly when the same has reached a desired depth; and thereafter driving said shielding pipe alone deeper into the ground so as to axially displace said shielding pipe relative to and forwardly of said drain pipe to thereby expose said apertures in the drain pipe while simultaneously forming an annular clearance about the drain pipe in which the soil is substantially spaced from said drain pipe.
 9. A method as defined in claim 8, wherein the step of suspending comprises suspending said drain pipe so that said leading end hangs at a slight upward inclination relative to the horizontal. 